Joern MCP Server

Instructions

Implementation Reference

• server_tools.py:67-75 (handler)

  The handler function implementing the 'get_class_methods_by_class_full_name' MCP tool. It is registered via the @joern_mcp.tool() decorator. The function sends a parameterized query to the Joern server using the joern_remote helper and parses the response into a list using extract_list.
  @joern_mcp.tool() def get_class_methods_by_class_full_name(class_full_name:str) -> list[str]: """Get the methods of a class by its fully qualified name @param class_full_name: The fully qualified name of the class @return: List of full name, name, signature and id of methods in the class """ response = joern_remote(f'get_class_methods_by_class_full_name("{class_full_name}")') return extract_list(response)
• server.py:94-106 (registration)

  The generate() function in server.py dynamically executes server_tools.py, which defines and registers the tool via its @joern_mcp.tool() decorator during server startup.
  SCRIPT_DIR = os.path.dirname(os.path.realpath(__file__)) GENERATED_PY = os.path.join(SCRIPT_DIR, "server_tools.py") def generate(): """Generate and execute additional server tools from server_tools.py file. This function reads the content of server_tools.py and executes it to add more functionality to the server. """ with open(GENERATED_PY, "r") as f: code = f.read() exec(compile(code, GENERATED_PY, "exec")) generate()
• server.py:38-71 (helper)

  The joern_remote helper function, called by the tool handler to execute the actual Joern query on the remote server.
  def joern_remote(query): """ Execute remote query and return results Parameters: query -- The query string to execute Returns: Returns the server response stdout content on success Returns None on failure, error message will be output to stderr """ data = {"query": query} headers = {'Content-Type': 'application/json'} try: response = requests.post( f'http://{server_endpoint}/query-sync', data=json.dumps(data), headers=headers, auth=basic_auth, timeout=timeout ) response.raise_for_status() result = response.json() return remove_ansi_escape_sequences(result.get('stdout', '')) except requests.exceptions.RequestException as e: sys.stderr.write(f"Request Error: {str(e)}\n") except json.JSONDecodeError: sys.stderr.write("Error: Invalid JSON response\n") return None
• common_tools.py:38-45 (helper)

  The extract_list helper function parses the Joern query response into a structured list of method information (fullName, name, signature, id). Used by the tool handler.
  def extract_list(input_str): """Extract a list of elements from a string representation of a Scala List. Parameters: input_str -- The input string containing a Scala List representation Returns: A Python list containing the extracted elements with cleaned data